Resource Allocation Optimization Using Variational Inequality In OFDM-Based Cognitive Radio Systems With Multiple Relays

Due to the spectrum scarcity and energy constraint of the nodes, how to employ spectrum and energy efficiently has become a primary challenge for multiuser OFDM-based cognitive radio (CR) systems with multiple relays. A single resource allocation (RA) is often used in traditional RA schemes, which may ignore the interference temperature limit. To improve the resource utilization, OFDM-based joint RA optimization model is often employed. The relay selection, the subcarrier pairs and powers of sources and relays are optimized jointly under the interference introduced to the primary system. This thesis focuses on the objective that maximizes the sum capacity by the best-relay selection and optimizing joint subcarrier and power allocation.Firstly, to solve the interference problem caused by the unbalanced energy employment, a best-relay selection using SNR and interference quotient for OFDM-based CR Systems with multiple relays is proposed. A best-relay system model in CR networks is constructed. An expected the interference threshold is predefined that secondary users satisfy stringent interference limit. A SNR threshold above a certain value is provided for relay link transmission quality. We get a set that the best relay lies in. We derive expressions for the quotient of the relay link SNR and the interference so as to choose the best relay from the set. We derive closed form expressions for the cumulative distribution function (CDF) of the total SNR at the destination using moment generating function (MGF) approach. To analyze system performance, we also derive closed form expressions for the outage probability and average bit error probability.Secondly, according to the competition and cooperation of the spectrum and energy among different types of nodes in the multiuser OFDM-based CR Systems with multiple relays, RA optimization using variational inequality (â…¥) is proposed. Considering direct link and relay link transmission at the same time, the equivalent channel gain is provided to simplify cooperative relay model to non-relay model. For multiuser joint RA problem under multiple constraints, a non-cooperative game (NCG) model is constructed. Introduce a pricing mechanism to solve the coupling among all the players introduced. There is an easy equivalence between a coupling NCG and a suitably defined â…¥. The monotonicity property of gradient vector function and symmetry of Jacobian matrix are proposed, which provide us with all the mathematical tools necessary to analyze the existence and uniqueness of the NE solution along with their convergence properties. A joint subcarrier and power allocation algorithm is formed with distributed iterative water-filling algorithm (IWFA) by constructing the Lagrange function.At last, performance evaluations of the proposed relay selection, subcarrier and power allocation of multiuser OFDM-based CR Systems with multiple relays are taken under MATLAB simulation, and the results show the reasonability of best-relay selection and joint RA optimization in multiuser OFDM-based CR Systems with multiple relays.